Tandy 1000 Technical Reference Manual

Tandy 1000
inter
Output Control Signal Definition
8255A18255A·5
Technical Reference Manual
MODE 1 (PORT A)
OBF (Output Buffer Full F/F). The OBF output will go
"low" to indicate that the CPU has written data out to
the specified port. The OBF F/F
will be set by the rising
edge of the WR input and reset by ACK Input being low.
ACK (Acknowledge Input). A "low" on this input informs
the 8255A that the data from port A or port B has been ac·
cepted.
In essence, a response from the peripheral
device indicating that it has received the data
output by
the
CPU.
INTR (Interrupt Request). A "high" on this output can be
used
to interrupt the CPU when an output device has ac-
cepted data
transmitted by the CPU. INTR is set when
ACK is a "one", OBF is a "one" and INTE is a "one". It is
reset by the falling edge of WR.
INTE A
Controlled by bit set/reset of PCG.
INTE B
Controlled by bit setlreset of PC2.
Figure 10. MODE 1 Output
Figure 11. Mode 1 (Strobed Output)
6-175
AFN.Q0744C

Tandy 1000 Specifications

General

Processor	Intel 8088
Processor Speed	4.77 MHz
RAM	128 KB (expandable to 640 KB)
Operating System	MS-DOS 2.11
Manufacturer	Tandy Corporation
Release Year	1984
Storage	Single or double 5.25" floppy disk drive (360 KB), optional hard drive
Sound	Tandy 3-voice sound
Ports	Parallel, Serial
Graphics	CGA (Color Graphics Adapter)
Graphics Modes	320x200, 640x200